> On 24 Jan 2019, at 09.35, Jan Kara <[email protected]> wrote: > > On Wed 23-01-19 19:27:12, Javier González wrote: >>> On 9 Jan 2019, at 16.30, Kanchan Joshi <[email protected]> wrote: >>> >>> Exiting write-hints are exposed to user-mode. There is a possiblity >>> of conflict if kernel happens to use those. This patch introduces four >>> write-hints for exclusive kernel-mode use. >>> >>> Signed-off-by: Kanchan Joshi <[email protected]> >>> --- >>> include/linux/fs.h | 5 +++++ >>> 1 file changed, 5 insertions(+) >>> >>> diff --git a/include/linux/fs.h b/include/linux/fs.h >>> index 811c777..e8548eb 100644 >>> --- a/include/linux/fs.h >>> +++ b/include/linux/fs.h >>> @@ -291,6 +291,11 @@ enum rw_hint { >>> WRITE_LIFE_MEDIUM = RWH_WRITE_LIFE_MEDIUM, >>> WRITE_LIFE_LONG = RWH_WRITE_LIFE_LONG, >>> WRITE_LIFE_EXTREME = RWH_WRITE_LIFE_EXTREME, >>> +/* below ones are meant for in-kernel use */ >>> + KERN_WRITE_LIFE_SHORT, >>> + KERN_WRITE_LIFE_MEDIUM, >>> + KERN_WRITE_LIFE_LONG, >>> + KERN_WRITE_LIFE_EXTREME >>> }; >> >> I think Jens and Dave meant kernel hints to go top down. This would also >> give space for supporting more hints / streams from both ends for user >> and kernel. > > Yes, that was the idea however if I understand it right, the write hints do > not really have to be consistent boot-to-boot since they aren't stored > persistently by the disk, are they? If that's the case, it doesn't really > matter which numbers we pick. >
I guess this is implementation specific. Some times the drive will want to store this to improve GC. For the current "coldness" hint I does not matter much, but if the hint were to express other metric it can become relevant. Anyway, the comment was more to separate user / kernel hints and allow them to grow from the ends. > One thing I don't quite like is the naming of KERN_WRITE_LIFE_SHORT etc.. It > is upto filesystem to assign meanings to the write hints. So I think it is > enough to provide something like KERN_WRITE_HINT_MIN which is the first > hint available to the kernel and then the number of hints available to the > kernel. > Makes sense to me. Then we can rename the hint for each FS to give it proper mening. > Honza > > -- > Jan Kara <[email protected]> > SUSE Labs, CR Javier
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